In audio applications and in particular in audio coding often a processing of subband signals is performed. Efficient filter banks are realised by using quadrature mirror filters QMF, or fast Fourier transform FFT use subbands with equal bandwidth. However, in audio applications and in audio coding it is advantageous that the used subbands have different bandwidths adapted to the psycho-acoustic properties of human hearing. Therefore in audio processing a number of subbands from the original filter bank are combined so as to form an adapted filter bank with subbands having different bandwidths. Alternatively, a group of adjacent subbands from the original filter bank is processed using the same parameters. In audio coding quantised parameters for each subband group are stored or transmitted.
There exist different scales (e.g. Bark scale) for the frequency axis that approximate the properties of human hearing, e.g.:    H. Traunmüller, “Analytical expressions for the tonotopic sensory scale”, The Journal of the Acoustical Society of America, vol. 88(1), pp. 97-100, 1990.    E. Zwicker, and H. Fastl, “Psychoacoustics: Facts and Models”, Springer series in information sciences, Springer, second updated edition, 1999.